05 dodge ram 1500 vehicle has delay in moving

After the vehicle (05 Ram 1500 with 142,000) has sat for a period of time (minutes to hours), when you start the truck and immediately put it into gear, it feels like the transmission is not engaging for a few seconds. I took the truck to a "certified" shop and they indicate that the truck is acting normal doing this. They sited a Dodge service bulletin that says that when the vehicle is turned off, the transmission fluid drains into the transfer case. When started, it takes 5+ seconds for the fluid to be pumped from the transfer case to the transmission thus the feeling of the transmission is slipping when the truck is started and immediately put into gear. They tell me that I need to start the truck, wait at least 5 seconds and then put into gear. True or false?